An ordinary refrigeration system for supermarket application uses multiples evaporators to refrigerate or to maintain in frozen conditions different perishable food products. The refrigerant vapors from the evaporators are fed to the refrigeration compressors, several in number, where through a mechanical compression their pressure and temperature are increased. The high pressure hot refrigerant vapors are fed to an outdoor air cooled condenser, where the latent heat of the refrigerant vapors is absorbed by the outdoor air and as a result the refrigerant vapors are liquified. This liquid is fed through expansion valves, thus reducing its temperature and pressure, to the evaporators, where the liquified refrigerant evaporates absorbing heat from the surrounding food products.
The pressure and the temperature of the refrigerant vapors condensing in the air cooled condenser are subject of the outdoor air temperature. During the cold period of the year, even if there is a possibility to reduce the condensing pressure, a high condensing pressure is maintained artificially in order to provide a sufficient pressure differential for the proper operation of the expansion valves; another reason for maintaining a high condensing pressure during the cold periods of the year is the use of heat reclaim coils to recuperate the heat of condensation and use it for comfort heating of the building. In order to obtain an efficient heat transfer in the heat reclaim coil, a substantial difference between the indoor air temperature and the condensing temperature is required which can be provided only by increasing the condensing pressure.
It is well known that the refrigeration compressor energy consumption efficiency is function of the ratio between the condensing pressure and the evaporating pressure. By lowering the condensing pressure, the refrigerant capacity of the compressor is increased and its power consumption decreased.
A new technology exists today (liquid delivery system) allowing the refrigeration system to work with floating condensing pressure depending on the outdoor air temperature. This is achieved by installing a centrifugal pump on the line of liquid refrigerant after the condenser, thus providing the necessary pressure differential for the proper operation of the expansion valves using a very small amount of energy. The condensing temperature could be reduced to 60.degree. F. depending on the outdoor air temperature.
The above mentioned technology produces energy savings up to 35% of the total energy cost but creates difficulties in the field of heat reclaim especially when a recuperation of the total condensing heat is required because the air to be heated is warmer then the refrigerant to be cooled. When a heat reclaim is required the condensing pressure has to be raised artificially in order to achieve proper heat transfer, thus losing the benefits of the liquid delivery system.